1. Technical Field
The present invention generally relates to wire termination techniques for twinax and shielded parallel pair wires used for high performance cables and in particular to methods that provide a low inductance path for the drain wire and shield of the twinax wire.
2. Description of the Related Art
Copper cables for digital communications use many different types of connectors, bulk wire, and wire termination techniques. While copper cables are used in a wide variety of applications, performance requirements for cables continue to increase to keep pace with integrated circuit technology performance increases. In order to meet the performance increases, many copper cables interfaces use low voltage differential signals that require a low skew and low cross-talk connector, bulk wire, and cable assembly construction.
The basic types of bulk wire used in I/O (input/output) cables includes ribbon, twisted pair, coax, twinax, and quad constructions. The preferred bulk wire construction for high speed differential cables is a xe2x80x9ctwinaxxe2x80x9d or shielded parallel pair wire. The parallel pair construction is optimized to provide low signal skew performance and the shielding surrounding the wire pair ensure low cross-talk between wire pairs, The shield of the twinax wire is stripped back to expose the insulated signal wires and the drain wire for termination processing. The length of shielding removed from the twinax wire has a significant effect on the shielding performance of the wire.
I/O connectors that are used in copper cables come in many shapes, sizes, and number of contacts. The number of contacts used in the connector is determined by the signal interface requirements. A differential serial interface would typically use a total of 4 signal contacts while a differential parallel interface would typically use a minimum of 36 signal contacts. Many of the current generation of I/O connectors use additional contacts connected to ground to enhance the performance of the connector interface. Ground blades or plates can be used instead of dedicated ground contacts to further enhance the performance of the connector. Most I/O connectors also include a metal shell that provides a connection from the braid shielding in the bulk wire and continuous 360 degree shield around the connector housing to minimize EMI radiation problems.
Typical wire termination techniques for copper cables include bare wire crimping, soldering, welding, and insulation displacement (IDC). Another wire termination technique that is often used for high speed cables includes a small printed circuit card or paddle card attached to the connector with the conductors in the bulk wire soldered to the paddle card. This type of wire termination provides a simple way to incorporate equalization in the cable assembly by adding chip capacitors and resistors to the circuitry on the paddle card.
FIG. 7 shows an isometric view of an I/O cable connector 700 attached to a small printed circuit card 704, in a conventional manner. The I/O cable connector 700 is comprised of an insulating plastic housing 702, a metal shell 703, and multiple conductive contacts 701. The ends of the contacts 701 in the connector 700 are soldered to the corresponding terminal pads 707 on the printed circuit card 704. The printed circuit card 704 also has multiple terminal pads 706 on the top 705 and bottom surfaces for wire terminations.
FIG. 8 shows an isometric view of multiple twinax wires 810 terminated to the printed circuit card 804 attached to the I/O cable connector 800, in a conventional manner. The twinax wires 810 are comprised of two parallel copper signal wires 812, 813 that are covered with insulating dielectric material 814, 815 and surrounded by a thin metallized shield 816. A third bare copper wire 811 or drain wire is located between the two insulated signal conductors 812, 813 and soldered to corresponding terminal pads 806 on the surface 805 of the printed circuit card 804. A portion of the metallized shield 816 is removed to expose the drain wire 811 and the insulation 814, 815 covering each of the signal conductors 812, 813 to allow soldering to the terminal pads 806 on the printed circuit card 804. A portion of the insulation 814,815 covering each of the signal wires 812, 813 is removed to allow soldering to the terminal pads 806 on the printed circuit card 804.
Impedance variations in the cable assembly can cause reflections in a high speed signal interface and result in data errors. Uniform geometry and materials in the bulk wire along with a gradual transition in geometry from the bulk wire to the wire termination and connector interface is essential to minimize impedance variations. Repeatability and consistency of the wire termination process has a similar effect.
Cross-talk from one signal to an adjacent signal or excessive skew between the two conductors of a differential signal can also result in data errors. It would therefore be desirable to provide individually shielded twinax construction, which would minimize cross-talk in the bulk wire and consistent dielectric material properties ensure low signal skew. Further, it would be desirable to provide dedicated ground pins, blades, or plates in the connector along with equal length differential signal wiring and a ground plane paddle card construction to further minimize the effects of cross-talk and skew in the connector and wire termination area.
It is therefore one object of the present invention to provide a technique for terminating multiple twinax wires with individual shields and drain wires.
It is another object of the present invention to provide a technique for minimizing the impedance discontinuity of the wire terminations.
It is yet another object of the present invention to provide a technique for minimizing the cross-talk in the wire termination area.
It is yet another object of the present invention to provide a low inductance connection from the drain wires on the individually shielded twinax wires to the ground connections in the cable connector.
It is yet an additional object of the present invention to provide a technique for terminating the twinax signal conductors directly to the terminals on the cable connector for applications that do not require equalization circuitry in the cable assembly.
The foregoing objects are achieved as is now described. The preferred embodiment provides a terminator assembly for a twinax wire. According to this embodiment, a PCB is provided which receives the twinax wire and provides a positive connection between a grounding bar of the PCB and the drain wide of the twinax pair. The drain wire is extended in an orthogonal direction to the twinax pair, and is engaged using an interference fit with the grounding bar. The grounding bar assembly also provides improved shielding for the twinax pair, where the integral shielding of the twinax wire has been removed to provide the connection. In an alternate embodiment, the terminating end of the twinax wire itself is encased in a termination clip. This clip provides shielding for the twinax pair, while electrically connecting with the twinax drain wire. The twinax wire, with the terminating clip, can then be easily attached to a connector PCB adapted to receive the terminator clip.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.